bad cap cause fuse to blow?

[paulmars]

microwave oven Fuse blew, replacement blew too after 1\2 second.

Following common resistance test procedures found on the web the magnetron and transformer are fine.

The big capacitor tests open. The diode attached to it reads mostly open in one direction, although sometimes my dvm will jump down to several meg ohms for a fraction of a second. Testing in other directions reads a constantly changing value of 5xxMeg to 8xxMeg.

Would these cause the fuse to blow?

Emerson mld mw8987b

Tks,
Paul

[R_J]

Re: bad cap cause fuse to blow?

In most cases when the fuse blows it is caused by a defective door switch. The primary interlock door switches is likely bad (stays closed) and when the interlock monitor switch closes it blows the fuse.
The primary switch should open when the door is open, and if this switch is shorted, when the door is opened the monitor switch shorts across the ac line to prevent the oven from operating with the door open.

[paulmars]

Re: bad cap cause fuse to blow?

switches tested ok. cap and diode test bad.

[R_J]

Re: bad cap cause fuse to blow?

You wont be able to check the diode with a regular multimeter unless the diode is dead short. it is a high voltage diode, it has several diode junctions stacked in series internally, the capacitor will check open, it is only a few microfarad, you would need a capacitor checker to test its value.
If you believe the problem is with the high voltage components, disconnect the high voltage transformer primary and see if the oven still blows the fuse.

[stj]

Re: bad cap cause fuse to blow?

you probably cant test the cap - many have a parallel discharge resister in them

[paulmars]

Re: bad cap cause fuse to blow?

Capacitor meter reads down to 0.1ufd and reads this cap at ol.

Unplugged transformer primary and microwave runs and fuse dont blow.

[R_J]

Re: bad cap cause fuse to blow?

Ok, then it is a fault in the high voltage section, I mentioned the switches because it is a common problem with microwave ovens.

[redwire]

Re: bad cap cause fuse to blow?

The microwave oven capacitor can go low value or open-circuit (blown pressure switch), either gives no/weak cooking.
The capacitor can also have a ground fault. If if arcs internally to the can that would blow the fuse. Check resistance to the can.
The diode doesn't test shorted, RG308/HV6X2PI "bi-directional diode protection" seems a little weird, shown as two back-back diodes inside, one 6kv other is 1.7kV. I think it's got a HV zener.

That leaves the magnetron. Do an inspection see if it is arcing or cracked.

Op cross-posted
https://www.electronicspoint.com/for...second.297189/
https://forum.appliancepartspros.com...ter-1-2-second